Steam reformers for the conversion of gaseous hydrocarbons with steam into synthesis gas chiefly consisting of carbon monoxide and hydrogen are known. The steam reformation process is described in principle, for example in Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Vol. 15, chapter “Gas Production”, section 2.2. The different types of tubular reactors proven for this process are discussed in section 2.2.3 of the same chapter. There are shown tubular reactors in which the burners are installed in the roof or in the side walls of the reformer housing. It should be noted in addition that variants with burners installed in the bottom of the housing, with flames directed vertically upwards into the housing, also are possible, as is mentioned e.g. in the document DE 2521683 A1.
For the uniform heating of all reformer tubes filled with a catalyst fixed bed, which are disposed in the reformer housing, the design and the arrangement of the channels for discharging the burner waste gases from the housing is very important. As shown in FIG. 6 of the above-mentioned Ullmann section 2.2.3, a proven design of the reformers consists in arranging the burners in the housing roof and the waste gas collecting channels at the bottom of the housing. The burners and the channels, each one opposite the other, are disposed between the rows of the reformer tubes. From the document DE 102011120938 A1 it also is known that it is possible to arrange the waste gas collecting channels directly below the bottom of the reformer housing. The bottom of the reformer housing at the same time forms the cover of the channels. Through openings in the cover, the burner waste gas passes from the reformer housing into the waste gas collecting channels. Via a collecting conduit the ends of the channels are connected with an apparatus for sucking off the waste gas, such as a blower or a chimney. The flow resistance which the waste gas stream is subject to within each of the channels leads to a pressure loss from the beginning of a channel to the end of a channel. Furthermore, the waste gas quantity sucked off cumulatively increases along the length of the channels, as via additional openings in the longitudinal directions of the channels additional burner waste gases are discharged from the reformer housing. This results in non-uniform turbulences in the burner waste gas, which are distributed along the channel length or in the bottom region of the reformer housing, and hence to a non-uniform heating of the reformer tubes.